Compressed air energy storage system utilizing two-phase flow to facilitate heat exchange

ABSTRACT

A compressed-air energy storage system according to embodiments of the present invention comprises a reversible mechanism to compress and expand air, one or more compressed air storage tanks, a control system, one or more heat exchangers, and, in certain embodiments of the invention, a motor-generator. The reversible air compressor-expander uses mechanical power to compress air (when it is acting as a compressor) and converts the energy stored in compressed air to mechanical power (when it is acting as an expander). In certain embodiments, the compressor-expander comprises one or more stages, each stage consisting of pressure vessel (the “pressure cell”) partially filled with water or other liquid. In some embodiments, the pressure vessel communicates with one or more cylinder devices to exchange air and liquid with the cylinder chamber(s) thereof. Suitable valving allows air to enter and leave the pressure cell and cylinder device, if present, under electronic control.

CROSS-REFERENCE TO RELATED APPLICATION

The instant nonprovisional patent application claims priority to U.S.Provisional Patent Application No. 61/221,487, filed Jun. 29, 2009 andincorporated by reference in its entirety herein for all purposes.

BACKGROUND

Air compressed to 300 bar has energy density comparable to that oflead-acid batteries and other energy storage technologies. However, theprocess of compressing and decompressing the air typically isinefficient due to thermal and mechanical losses. Such inefficiencylimits the economic viability of compressed air for energy storageapplications, despite its obvious advantages.

It is well known that a compressor will be more efficient if thecompression process occurs isothermally, which requires cooling of theair before or during compression. Patents for isothermal gas compressorshave been issued on a regular basis since 1930 (e.g., U.S. Pat. No.1,751,537 and No. 1,929,350). One approach to compressing airefficiently is to effect the compression in several stages, each stagecomprising a reciprocating piston in a cylinder device with anintercooler between stages (e.g., U.S. Pat. No. 5,195,874). Cooling ofthe air can also be achieved by injecting a liquid, such as mineral oil,refrigerant, or water into the compression chamber or into the airstreambetween stages (e.g., U.S. Pat. No. 5,076,067).

Several patents exist for energy storage systems that mix compressed airwith natural gas and feed the mixture to a combustion turbine, therebyincreasing the power output of the turbine (e.g., U.S. Pat. No.5,634,340). The air is compressed by an electrically-driven aircompressor that operates at periods of low electricity demand. Thecompressed-air enhanced combustion turbine runs a generator at times ofpeak demand. Two such systems have been built, and others proposed, thatuse underground caverns to store the compressed air.

Patents have been issued for improved versions of this energy storagescheme that apply a saturator upstream of the combustion turbine to warmand humidify the incoming air, thereby improving the efficiency of thesystem (e.g., U.S. Pat. No. 5,491,969). Other patents have been issuedthat mention the possibility of using low-grade heat (such as waste heatfrom some other process) to warm the air prior to expansion, alsoimproving efficiency (e.g., U.S. Pat. No. 5,537,822).

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention relate generally to energy storagesystems, and more particularly, relates to energy storage systems thatutilize compressed air as the energy storage medium, comprising an aircompression/expansion mechanism, a heat exchanger, and one or more airstorage tanks.

According to embodiments of the present invention, a compressed-airenergy storage system is provided comprising a reversible mechanism tocompress and expand air, one or more compressed air storage tanks, acontrol system, one or more heat exchangers, and, in certain embodimentsof the invention, a motor-generator.

The reversible air compressor-expander uses mechanical power to compressair (when it is acting as a compressor) and converts the energy storedin compressed air to mechanical power (when it is acting as anexpander). The compressor-expander comprises one or more stages, eachstage consisting of pressure vessel (the “pressure cell”) partiallyfilled with water or other liquid. In some embodiments, the pressurevessel communicates with one or more cylinder devices to exchange airand liquid with the cylinder chamber(s) thereof. Suitable valving allowsair to enter and leave the pressure cell and cylinder device, ifpresent, under electronic control.

The cylinder device referred to above may be constructed in one ofseveral ways. In one specific embodiment, it can have a piston connectedto a piston rod, so that mechanical power coming in or out of thecylinder device is transmitted by this piston rod. In anotherconfiguration, the cylinder device can contain hydraulic liquid, inwhich case the liquid is driven by the pressure of the expanding air,transmitting power out of the cylinder device in that way. In such aconfiguration, the hydraulic liquid can interact with the air directly,or a diaphragm across the diameter of the cylinder device can separatethe air from the liquid.

In low-pressure stages, liquid is pumped through an atomizing nozzleinto the pressure cell or, in certain embodiments, the cylinder deviceduring the expansion or compression stroke to facilitate heat exchange.The amount of liquid entering the chamber is sufficient to absorb(during compression) or release (during expansion) all the heatassociated with the compression or expansion process, allowing thoseprocesses to proceed near-isothermally. This liquid is then returned tothe pressure cell during the non-power phase of the stroke, where it canexchange heat with the external environment via a conventional heatexchanger. This allows the compression or expansion to occur at highefficiency.

Operation of embodiments according the present invention may becharacterized by a magnitude of temperature change of the gas beingcompressed or expanded. According to one embodiment, during acompression cycle the gas may experience an increase in temperate of 100degrees Celsius or less, or a temperature increase of 60 degrees Celsiusor less. In some embodiments, during an expansion cycle, the gas mayexperience a decrease in temperature of 100 degrees Celsius or less, 15degrees Celsius or less, or 11 degrees Celsius or less—nearing thefreezing point of water from an initial point of room temperature.

Instead of injecting liquid via a nozzle, as described above, air may bebubbled though a quantity of liquid in one or more of the cylinderdevices in order to facilitate heat exchange. This approach is preferredat high pressures.

During expansion, the valve timing is controlled electronically so thatonly so much air as is required to expand by the desired expansion ratiois admitted to the cylinder device. This volume changes as the storagetank depletes, so that the valve timing must be adjusted dynamically.

The volume of the cylinder chambers (if present) and pressure cellsincreases from the high to low pressure stages. In other specificembodiments of the invention, rather than having cylinder chambers ofdifferent volumes, a plurality of cylinder devices is provided withchambers of the same volume are used, their total volume equating to therequired larger volume.

During compression, a motor or other source of shaft torque drives thepistons or creates the hydraulic pressure via a pump which compressesthe air in the cylinder device. During expansion, the reverse is true.Expanding air drives the piston or hydraulic liquid, sending mechanicalpower out of the system. This mechanical power can be converted to orfrom electrical power using a conventional motor-generator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of the first embodiment of acompressed air energy storage system in accordance with the presentinvention, that is a single-stage, single-acting energy storage systemusing liquid mist to effect heat exchange.

FIG. 2 is a block diagram of a second embodiment of a compressed airenergy storage system showing how multiple stages are incorporated intoa complete system in accordance with the present invention.

FIG. 3 is a schematic representation of a third embodiment of acompressed air energy storage system, that is a single-stage,single-acting energy storage system that uses both liquid mist and airbubbling through a body of liquid to effect heat exchange.

FIG. 4 is a schematic representation of a one single-acting stage thatuses liquid mist to effect heat exchange in a multi-stage compressed airenergy storage system in accordance with the present invention.

FIG. 5 is a schematic representation of one double-acting stage in amulti-stage compressed air energy storage system in accordance with thepresent invention.

FIG. 6 is a schematic representation of one single-acting stage in amulti-stage compressed air energy storage system, in accordance with thepresent invention, that uses air bubbling through a body of liquid toeffect heat exchange.

FIG. 7 is a schematic representation of a single-acting stage in amulti-stage compressed air energy storage system, in accordance with thepresent invention, using multiple cylinder devices.

FIG. 8 is a schematic representation of four methods for conveying powerinto or out of the system.

FIG. 9 is a block diagram of a multi-stage compressed air energy systemthat utilizes a hydraulic motor as its mechanism for conveying andreceiving mechanical power.

FIG. 10 shows an alternative embodiment of an apparatus in accordancewith the present invention.

FIGS. 11A-11F show operation of the controller to control the timing ofvarious valves.

FIGS. 12A-C show the configuration of an apparatus during steps of acompression cycle according to an embodiment of the present invention.

FIGS. 13A-C show the configuration of an apparatus during steps of anexpansion cycle according to an embodiment of the present invention.

FIGS. 14A-C show the configuration of an apparatus during steps of acompression cycle according to an embodiment of the present invention.

FIGS. 15A-C show the configuration of an apparatus during steps of anexpansion cycle according to an embodiment of the present invention.

FIGS. 16A-D show the configuration of an apparatus during steps of acompression cycle according to an embodiment of the present invention.

FIGS. 17A-D show the configuration of an apparatus during steps of anexpansion cycle according to an embodiment of the present invention.

FIGS. 18A-D show the configuration of an apparatus during steps of acompression cycle according to an embodiment of the present invention.

FIGS. 19A-D show the configuration of an apparatus during steps of anexpansion cycle according to an embodiment of the present invention.

FIG. 20 shows a simplified view of a computer system suitable for use inconnection with the methods and systems of the embodiments of thepresent invention.

FIG. 20A is an illustration of basic subsystems in the computer systemof FIG. 20.

FIG. 21 is an embodiment of a block diagram showing inputs and outputsto a controller responsible for controlling operation of variouselements of an apparatus according to the present invention.

While certain drawings and systems depicted herein may be configuredusing standard symbols, the drawings have been prepared in a moregeneral manner to reflect the variety of implementations that may berealized from different embodiments.

DETAILED DESCRIPTION OF THE INVENTION

While the present invention will be described with reference to a fewspecific embodiments, the description is illustrative of the inventionand is not to be construed as limiting the invention. Variousmodifications to the present invention can be made to the preferredembodiments by those skilled in the art without departing from the truespirit and scope of the invention. It will be noted here that for abetter understanding, like components are designated by like referencenumerals throughout the various figures.

Single-Stage System

FIG. 1 depicts the simplest embodiment of the compressed air energystorage system 20 of the present invention, and illustrates many of theimportant principles. Briefly, some of these principles which improveupon current compressed air energy storage system designs include mixinga liquid with the air to facilitate heat exchange during compression andexpansion, thereby improving the efficiency of the process, and applyingthe same mechanism for both compressing and expanding air. Lastly, bycontrolling the valve timing electronically, the highest possible workoutput from a given volume of compressed air can be obtained.

As best shown in FIG. 1, the energy storage system 20 includes acylinder device 21 defining a chamber 22 formed for reciprocatingreceipt of a piston device 23 or the like therein. The compressed airenergy storage system 20 also includes a pressure cell 25 which whentaken together with the cylinder device 21, as a unit, form a one stagereversible compression/expansion mechanism (i.e., a one-stage 24). Thereis an air filter 26, a liquid-air separator 27, and a liquid, tank 28,containing a liquid 49 d fluidly connected to the compression/expansionmechanism 24 on the low pressure side via pipes 30 and 31, respectively.On the high pressure side, an air storage tank or tanks 32 is connectedto the pressure cell 25 via input pipe 33 and output pipe 34. Aplurality of two-way, two position valves 35-43 are provided, along withtwo output nozzles 11 and 44. This particular embodiment also includesliquid pumps 46 and 47. It will be appreciated, however, that if theelevation of the liquid tank 28 is higher than that of the cylinderdevice 21, water will feed into the cylinder device by gravity,eliminating the need for pump 46.

Briefly, atmospheric air enters the system via pipe 10, passes throughthe filter 26 and enters the cylinder chamber 22 of cylinder device 21,via pipe 30, where it is compressed by the action of piston 23, byhydraulic pressure, or by other mechanical approaches (see FIG. 8).Before compression begins, a liquid mist is introduced into the chamber22 of the cylinder device 21 using an atomizing nozzle 44, via pipe 48from the pressure cell 25. This liquid may be water, oil, or anyappropriate liquid 49 f from the pressure cell having sufficient highheat capacity properties. The system preferably operates atsubstantially ambient temperature, so that liquids capable ofwithstanding high temperatures are not required. The primary function ofthe liquid mist is to absorb the heat generated during compression ofthe'air in the cylinder chamber. The predetermined quantity of mistinjected into the chamber during each compression stroke, thus, is thatrequired to absorb all the heat generated during that stroke. As themist condenses, it collects as a body of liquid 49 e in the cylinderchamber 22.

The compressed air/liquid mixture is then transferred into the pressurecell 25 through outlet nozzle 11, via pipe 51. In the pressure cell 25,the transferred mixture exchanges the captured heat generated bycompression to a body of liquid 49 f contained in the cell. The airbubbles up through the liquid and on to the top of the pressure cell,and then proceeds to the air storage tank 32, via pipe 33.

The expansion cycle is essentially the reverse process of thecompression cycle. Air leaves the air storage tank 32, via pipe 34,bubbling up through the liquid 49 f in the pressure cell 25, enters thechamber 22 of cylinder device 21, via pipe 55, where it drives piston 23or other mechanical linkage. Once again, liquid mist is introduced intothe cylinder chamber 22, via outlet nozzle 44 and pipe 48, duringexpansion to keep a substantially constant temperature in the cylinderchamber during the expansion process. When the air expansion iscomplete, the spent air and mist pass through an air-liquid separator 27so that the separated liquid can be reused. Finally, the air isexhausted to the atmosphere via pipe 10.

The liquid 49 f contained in the pressure cell 25 is continuallycirculated through the heat exchanger 52 to remove the heat generatedduring compression or to add the heat to the chamber to be absorbedduring expansion. This circulating liquid in turn exchanges heat with athermal reservoir external to the system (e.g. the atmosphere, a pond,etc.) via a conventional air or water-cooled heat exchanger (not shownin this figure, but shown as 12 in FIG. 3). The circulating liquid isconveyed to and from that external heat exchanger via pipes 53 and 54communicating with internal heat exchanger 52.

The apparatus of FIG. 1 further includes a controller/processor 1004 inelectronic communication with a computer-readable storage device 1002,which may be of any design, including but not limited to those based onsemiconductor principles, or magnetic or optical storage principles.Controller 1004 is shown as being in electronic communication with auniverse of active elements in the system, including but not limited tovalves, pumps, chambers, nozzles, and sensors. Specific examples ofsensors utilized by the system include but are not limited to pressuresensors (P) 1008, 1014, and 1024, temperature sensors (T) 1010, 1018,1016, and 1026, humidity sensor (H) 1006, volume sensors (V) 1012 and1022, and flow rate sensor 1020.

As described in detail below, based upon input received from one or moresystem elements, and also possibly values calculated from those inputs,controller/processor 4 may dynamically control operation of the systemto achieve one or more objectives, including but not limited tomaximized or controlled efficiency of conversion of stored energy intouseful work; maximized, minimized, or controlled power output; anexpected power output; an expected output speed of a rotating shaft incommunication with the piston; an expected output torque of a rotatingshaft in communication with the piston; an expected input speed of arotating shaft in communication with the piston; an expected inputtorque of a rotating shaft in communication with the piston; a maximumoutput speed of a rotating shaft in communication with the piston; amaximum output torque of a rotating shaft in communication with thepiston; a minimum output speed of a rotating shaft in communication withthe piston; a minimum output torque of a rotating shaft in communicationwith the piston; a maximum input speed of a rotating shaft incommunication with the piston; a maximum input torque of a rotatingshaft in communication with the piston; a minimum input speed of arotating shaft in communication with the piston; a minimum input torqueof a rotating shaft in communication with the piston; or a maximumexpected temperature difference of air at each stage.

The compression cycle for this single-stage system proceeds as follows:

Step 1 2 3 4 5 Description Add Add Compress Move Refill liquid to mistto compressed cylinder cylinder cylinder air to device device devicepressure cell Valve 35 Open Closed Closed Closed Closed Valve 36 OpenClosed Closed Closed Open Valve 37 Closed Closed Closed Closed ClosedValve 38 Closed Closed Closed Open Closed Valve 39 Closed Open ClosedClosed Closed Valve 40 Closed Closed Closed Closed Closed Valve 41Closed Closed Closed Open Closed Valve 42 Open Closed Closed ClosedClosed Valve 43 Closed Closed Closed Closed Open Pump 46 On Off Off OffOff Pump 47 Off On Off Off Off Piston 23 Near Near At BDC at Between AtTDC at bottom BDC start of BDC and start of dead step TDC step center(BDC)

During step 1 of the compression cycle, liquid 49 d is added to thechamber 22 of the cylinder device 21 from the liquid tank 28 (collectingas body of liquid 49 e) such that, when the piston 23 reaches top deadcenter (TDC), the dead volume in the cylinder device is zero. This willonly have to be done occasionally, so that this step is omitted on thegreat majority of cycles.

During step 2 of the compression cycle, liquid mist from pressure cell25 is pumped, via pump 47, into the cylinder chamber 22, via pipe 48 andnozzle 44. The selected quantity of mist is sufficient to absorb theheat generated during the compression step (step 3). The volume fractionof liquid must sufficiently low enough that the droplets will notsubstantially fuse together, thus reducing the effective surface areaavailable for heat exchange (that is, the interface between air andliquid). Typically, the pressure differential between the pressure cell25 and the chamber 22 of the cylinder device 21 is sufficiently high sothat the operation of pump 47 is not required.

During step 3 of the compression cycle, the piston 23 is driven upwardby a crankshaft (not shown) coupled to a piston rod 19, by hydraulicpressure, or by some other mechanical structure (as shown in FIG. 8),compressing the air and mist contained in the cylinder chamber.

Step 4 of the compression cycle begins when the air pressure inside thecylinder chamber 22 is substantially equal to the pressure inside thepressure cell 25, at which point outlet valve 38 opens, allowingcompressed air to flow from the cylinder chamber to the pressure cell.Because of the liquid added to the cylinder device during step 1 of thecompression cycle, substantially all the air in the cylinder chamber canbe pushed out during this step. The compressed air is introduced intothe pressure cell 25 through an inlet nozzle 11, along with anyentrained mist, creating fine bubbles so that the heat generated duringcompression will exchange with the liquid 49 f in the cell rapidly.

During step 5 of the compression cycle, the piston 23 is pulled downallowing low-pressure air to refill it, via valve 36 and pipe 30. Theabove table shows valve 39 as being closed during this step, and showspump 47 as being off during this step 5. However, this is not required.In other embodiments valve 39 could be open and pump 47 could be on,during the step 5 such that mist is introduced into the cylinder chamberas it is refilled with air.

The expansion cycle for this single-stage system proceeds as follows:

Step 1 2 3 4 Description Add liquid to Add compressed Expansion Exhaustcylinder air and liquid spent air device mist to cylinder device Valve35 Open Closed Closed Closed Valve 36 Open Closed Closed Open Valve 37Closed Open Closed Closed Valve 38 Closed Closed Closed Closed Valve 39Closed Open Closed Closed Valve 40 Closed Open Closed Closed Valve 41Closed Closed Closed Closed Valve 42 Closed Closed Closed Open Valve 43Closed Closed Closed Closed Pump 46 On Off Off Off Pump 47 Off On OffOff Piston 23 Near TDC At TDC at start Near TDC at At BDC of step startof step at start of step

During step 1 of the expansion cycle, liquid is added to the cylinderchamber from the liquid tank 28 to eliminate dead volume in the system.This will be required only rarely, as mentioned above. Similar to thecompression cycle, the pump 46 can be eliminated if the liquid tank 28is oriented at an elevation higher than that of the chamber of cylinderdevice 21.

During step 2 of the expansion cycle, a pre-determined amount of air,V₀, is added to the chamber of the cylinder device by opening inletvalve 37 for the correct interval, which is dependent on the pressure ofthe air in the pressure cell and the desired expansion ratio. The V₀required is the total cylinder device volume divided by the desiredexpansion ratio. For a single stage system, that ratio is less than orequal to the pressure of air in the air storage tank in atmospheres. Atthe same time air is being introduced into the cylinder chamber 22,liquid mist from the pressure cell is being pumped (via pump 47) throughinlet nozzle 44 into the cylinder chamber. If a sufficient pressuredifferential exists between the pressure cell 25 and the cylinder device21, pump 47 is not required. Once the pressure inside of the cylinderchamber is sufficiently high, valve 37 is closed. The piston 23 is urgedin the direction of BDC beginning with this step, transmitting power outof the system via a crankshaft, hydraulic pressure, or other mechanicalstructure.

During step 3 of the expansion cycle, the air introduced in step 2 isallowed to expand in the chamber 22. Liquid mist also continues to bepumped into the chamber 22 through nozzle 44. The predetermined totalamount of mist introduced is that required to add enough heat to thesystem to keep the temperature substantially constant during airexpansion. The piston 23 is driven to the bottom of the cylinder deviceduring this step.

It will be appreciated that this two-step expansion process (a quantityof air V₀ introduced in the first step—step 2—and then allowed to expandin the second step—step 3) allows the system to extract substantiallyall the energy available in the compressed air.

During step 4 of the expansion cycle, the crankshaft or other mechanicallinkage moves the piston 19 back up to top dead-center (TDC), exhaustingthe spent air and liquid mist from the cylinder device. The powerrequired to drive the piston comes from the momentum of the systemand/or from the motion of other out-of-phase pistons. The exhausted airpasses through an air-liquid separator, and the liquid that is separatedout is returned to the liquid tank 28.

It will be appreciated that in accordance with the present invention, atany given time, energy is either being stored or delivered. The twoprocesses are never carried out simultaneously. As a result, the samemechanism can be used for both compression and expansion, reducingsystem cost, size and complexity. This is also the situation with all ofthe other embodiments of the present invention to be described below.

Multi-Stage System

When a larger compression/expansion ratio is required than can beaccommodated by the mechanical or hydraulic approach by which mechanicalpower is conveyed to and from the system, then multiple stages should beutilized. A multi-stage compressed air energy storage system 20 withthree stages (i.e., first stage 24 a, second stage 24 b and third stage24 c) is illustrated in schematic form in FIG. 2. Systems with more orfewer stages are constructed similarly. Note that, in all figures thatfollow, when the letters a, b, and c are used with a number designation(e.g. 25 a), they refer to elements in an individual stage of amulti-stage energy storage system 20.

In accordance with the present invention, each stage may typically havesubstantially the same expansion ratio. A stage's expansion ratio, r₁,is the Nth root of the overall expansion ratio. That is,

$r = \sqrt[N]{R}$

Where R is the overall expansion ratio and N is the number of stages. Itwill be appreciated, however, that the different stages can havedifferent expansion ratios, so long as the product of the expansionratios of all of the stages is R. That is, in a three-stage system, forexample:

r ₁ ×r ₂ ×r ₃ =R.

In order for the mass flow rate through each stage to be substantiallythe, the lower pressure stages will need to have cylinder chambers withgreater displacements. In a multi-stage system, the relativedisplacements of the cylinder chambers are governed by the followingequation:

$V_{i} = {V_{f}\frac{r^{i}}{\sum\limits_{j = 1}^{N}r^{j}}}$

Where V_(i) is the volume of the i^(th) cylinder device, and V_(f) isthe total displacement of the system (that is, the sum of thedisplacements of all of the cylinder devices).

As an example, suppose that the total displacement of a three-stagesystem is one liter. If the stroke length of each piston issubstantially the same and substantially equal to the bore (diameter) ofthe final cylinder chamber, then the volumes of the three cylinderchambers are about 19 cm³, 127 cm³, and 854 cm³. The bores are about1.54 cm, 3.96 cm, and 10.3 cm, with a stroke length of about 10.3 cm forall three. The lowest-pressure cylinder device is the largest and thehighest-pressure cylinder device the smallest.

FIG. 9 is a schematic representation of how three stages 24 a, 24 b and24 c could be coupled to a hydraulic system (e.g., a hydraulic motor 57and six hydraulic cylinders 61 a 1-61 c 2) to produce continuousnear-uniform power output. Each compressed-air-driven piston 23 a 1-23 c2 of each corresponding compressed-air driven cylinder device 21 a 1-21c 2 is coupled via a respective piston rod 19 a 1-19 c 2 to acorresponding piston 60 a 1-60 c 2 of a respective hydraulic cylinderdevice 61 a 1-61 c 2.

The chambers of the air-driven cylinder devices 21 a 1-21 c 2 vary indisplacement as described above. The chambers of the hydraulic cylinderdevices 61 a 1-61 c 2, however, are substantially identical indisplacement. Because the force generated by each air-driven piston issubstantially the same across the three stages, each hydraulic cylinderdevice provides substantially the same pressure to the hydraulic motor57. Note that, in this configuration, the two air-driven pistons 21 a 1,21 a 2 that comprise a given stage (e.g. the first stage 24 a) operate180 degrees out of phase with each other.

Stages Using Liquid Mist to Effect Heat Exchange in a Multi-Stage System

If a stage is single-acting and uses liquid mist to effect heatexchange, it operates according to the scheme described in the sectiontitled Single-Stage System above. Each single-acting stage of amulti-stage system 20 (e.g., the second stage 24 b of FIG. 2) isillustrated schematically in FIG. 4. In this configuration, air passesto a cylinder chamber 22 b of the second stage 24 b illustrated from thepressure cell 25 a of the next-lower-pressure stage (e.g., first stage24 a) during compression, and to the pressure cell of thenext-lower-pressure stage during expansion, via pipe 92 a/90 b. Liquidpasses to and from the pressure cell 25 a of the next-lower-pressurestage via pipe 93 a/91 b.

In contrast, air passes from pressure cell 25 b of the stage illustrated(e.g., the second stage 24 b) to the chamber of the cylinder device ofthe next higher-pressure stage (e.g., the third stage 24 c) duringcompression and from the chamber of the cylinder device of the nexthigher-pressure stage during expansion via pipe 92 b/90 c. It will beappreciated that the air compression/expansion mechanism (i.e., secondstage 24 b) illustrated is precisely the same as the central elements(the cylinder device 21 and the pressure cell 25 of the first stage 24)shown in FIG. 1, with the exception that, in FIG. 4, there is a pipe 93b that conveys liquid from the pressure cell of one stage to the chamberof the cylinder device of the next higher-pressure stage. Pipe 93 b isnot required for the highest-pressure stage; hence, it doesn't appear inthe diagrams, FIGS. 1 and 3, of single-stage configurations.

If the stage illustrated is the lowest-pressure-stage (e.g., first stage24 a in the embodiment of FIG. 2), then line 90 a passes air to anair-liquid separator (e.g., separator 27 in FIG. 1) during the expansioncycle and from an air filter (e.g., filter 26 in FIG. 1) during thecompression cycle. Similarly, if the stage illustrated is thelowest-pressure stage, then line 91 a communicates liquid to and fromthe liquid tank. If the stage illustrated is the highest-pressure-stage(e.g., the third stage 24 c), then air is conveyed to and from the airtank (e.g., air tank 32 in FIG. 1) via pipe 92 c.

Single-Acting Stage Utilizing Bubbles to Effect Heat Exchange

Instead of using liquid mist sprayed into the cylinder device orpressure cell in order to cool the air as it compresses or warm it as itexpands, one specific embodiment of the present invention utilizes theinverse process. As best illustrated in FIG. 6, that is, the air isbubbled up through a body of liquid 49 c 1 in the chamber 22 c of thecylinder device 21 c. This process should be used in preference to themist approach above discussed when the volume fraction of mist requiredto effect the necessary heat exchange would be sufficiently high enoughto cause a high percentage of the droplets to fuse during thecompression cycle. Typically, this occurs at higher pressures. Hence,the use of the designator c in FIG. 6 (e.g. 25 c) indicating a third, orhigh-pressure stage.

As described above in connection with FIG. 1, the apparatus of FIG. 6further includes a controller/processor 6002 in electronic communicationwith a computer-readable storage device 6004, which may be of anydesign, including but not limited to those based on semiconductorprinciples, or magnetic or optical storage principles. Controller 6002is shown as being in electronic communication with a universe of activeelements in the system, including but not limited to valves, pumps,chambers, nozzles, and sensors. Specific examples of sensors utilized bythe system include but are not limited to pressure sensors (P) 6008 and6014, temperature sensor (T) 6010, 6016, and 6018, and volume sensor (V)6012.

FIG. 6 illustrates a stage that uses bubbles to facilitate heatexchange. The compression cycle for this single-acting stage systemproceeds as follows:

Step 1 2 3 4 Description Fill cylinder Compress Transfer air toReplenish device with air pressure cell liquid Valve 108c Closed ClosedClosed Closed Valve 109c Closed Closed Open Closed Valve 114c ClosedClosed Closed Closed Valve 41c Closed Closed Open Closed Valve 40cClosed Closed Closed Closed Valve 106c Open Closed Closed Closed Valve110c Closed Closed Closed Closed Valve 111c Closed Closed Closed OpenPump 105c On Off Off Off Pump 113c Off Off Off On Piston 23c At top ofliquid At TDC at Near BDC at At BDC at start of step start of step startof step at start of step

In contrast, the expansion cycle for this single-acting stage systemuses the following process:

Step 1 2 3 4 Description Replenish Add compressed Expansion Exhaustliquid in air to cylinder spent air cylinder device device Valve 108cClosed Closed Closed Open Valve 109c Closed Closed Closed Closed Valve114c Closed Open Closed Closed Valve 41c Closed Closed Closed ClosedValve 40c Closed Open Closed Closed Valve 106c Closed Closed ClosedClosed Valve 110c Open Closed Closed Closed Valve 111c Closed ClosedClosed Closed Pump 105c Off Off Off Off Pump 113c On Off Off Off Piston23c At BDC at start At top of liquid Near BDC At TDC at start at start

An air-liquid mixture from the chamber 22 c of cylinder device 21 c inthis stage (e.g., third stage 24 c) is conveyed to the pressure cell 25b of the next lower-pressure stage (e.g., second stage 24 b) during theexpansion cycle, via valve 108 c and pipe 91 c/95 b. Air is conveyed tothe chamber 22 c of cylinder device 21 c in this third stage 24 c, forexample, from the next lower-pressure stage 24 b during compression viapipe 92 b/90 c.

In contrast, air from the pressure cell 25 c of this second stage 24 c,for instance, is conveyed to and from the cylinder chamber 22 d of nexthigher-pressure stage via pipe 92 c/90 d together with the operation ofin-line valve 41 c. Liquid 49 c from the pressure cell 25 c of thisstage is conveyed to the cylinder chamber 22 d of the nexthigher-pressure stage 24 d, for example, via pipe 93 c/94 d. Anair-liquid mixture from the cylinder chamber 22 d of the nexthigher-pressure stage (during the expansion cycle thereof) is conveyedto pressure cell 25 c of this stage via pipe 91 d/95 c.

It will be appreciated that, in some multi-stage systems, some(lower-pressure) stages might employ the liquid mist technique whileother (higher-pressure) stages may employ the bubbles technique to storeand remove energy therefrom.

Multiple Phases

The systems as described so far represent a single phase embodiment.That is, all pistons operate together over the course of one cycle.During expansion, for example, this produces a varying amount ofmechanical work output during one half of the cycle and requires somework input during the other half of the cycle. Such work input may befacilitated by the use of a flywheel (not shown).

To smooth out the power output over the course of one cycle and reducethe flywheel requirements, in one embodiment, multiple systems phasesmay be employed. N sets of pistons thus may be operated 360/N degreesapart. For example, four complete sets of pistons may be operated 90degrees out of phase, smoothing the output power and effectingself-starting and a preferential direction of operation. Note thatvalves connecting cylinder devices to a pressure cell are only openedduring less than one-half of a cycle, so it is possible to share apressure cell between two phases 180 degrees apart.

If N phases are used, and N is even, pairs of phases are 180 degreesapart and may be implemented using double-acting pistons. FIG. 5illustrates a double-acting stage that uses liquid mist to effect heatexchange. Each half of the piston operates according the protocoloutlined in the section Single Stage System, but 180 degrees out ofphase.

As described above in connection with FIG. 1, the apparatus of FIG. 5further includes a controller/processor 5002 in electronic communicationwith a computer-readable storage device 5004. which may be of anydesign, including but not limited to those based on semiconductorprinciples, or magnetic or optical storage principles. Controller 5002is shown as being in electronic communication with a universe of activeelements in the system, including but not limited to valves, pumps,chambers, nozzles, and sensors. Specific examples of sensors utilized bythe system include but are not limited to pressure sensors (P),temperature sensors (T), humidity sensor (H), and volume sensors (V).

The compression cycle for the double-acting stage illustrated in FIG. 5proceeds as follows:

Step 1 2 3 4 5 Description Add mist to Compress air Move air to Refillchamber Replenish chamber 22b1 in chamber pressure cell 22b1 and liquidsin and move air 22b1 and from chamber compress air in cylinder topressure refill chamber 22b1 and add chamber 22b2 device cell from 22b2mist to chamber 22b2 chamber 22b2 Valve 35b1 Closed Closed Open OpenClosed Valve 36b1 Closed Closed Closed Closed Open Valve 37b1 ClosedClosed Closed Closed Closed Valve 38b1 Closed Closed Open Closed ClosedValve 39b1 Open Closed Closed Closed Closed Valve 35b2 Open Open ClosedClosed Closed Valve 36b2 Closed Closed Closed Closed Open Valve 37b2Closed Closed Closed Closed Closed Valve 38b2 Open Closed Closed ClosedClosed Valve 39b2 Closed Closed Open Closed Closed Valve 40b ClosedClosed Closed Closed Closed Valve 41b Open Closed Open Closed ClosedPump 47b On Off On Off Off Piston 23b Near TDC at Between TDC Near BDCat Between TDC Between start of step and BDC, start of step and BDC, TDCand moving down moving up BDC

Note that step 5 is unnecessary, in some specific embodiments, and canbe omitted in the great majority of cycles since the liquid levels inthe piston remain substantially the same across long periods ofoperation.

In contrast, the expansion cycle for the double-acting stage illustratedin FIG. 5 proceeds as follows:

Step 1 2 3 4 5 Description Add mist and Allow air in Add mist and Allowair in Replenish air to chamber chamber 22b1 air to chamber chamber 22b2liquids in 22b1 and to expand and 22b2 and to expand and cylinderexhaust air continue exhaust air continue device from chamber exhaustingair from chamber exhausting air 22b2 from chamber 22b1 from chamber 22b222b1 Valve 35b1 Closed Closed Open Open Closed Valve 36b1 Closed ClosedClosed Closed Open Valve 37b1 Open Closed Closed Closed Closed Valve38b1 Closed Closed Closed Closed Closed Valve 39b1 Open Closed ClosedClosed Closed Valve 35b2 Open Open Closed Closed Closed Valve 36b2Closed Closed Closed Closed Open Valve 37b2 Closed Closed Open ClosedClosed Valve 38b2 Closed Closed Closed Closed Closed Valve 39b2 ClosedClosed Open Closed Closed Valve 40b Open Closed Open Closed Closed Valve41b Closed Closed Closed Closed Closed Pump 47b On Off On Off Off Piston23b Near TDC at Between TDC Near BDC at Between TDC Between start ofstep and BDC, start of step and BDC, TDC and moving down moving up BDC

Note that, as with compression, step 5 is rarely necessary and can beomitted in the great majority of cycles.

Stares with Multiple Cylinder Devices

If it is desirable that all the cylinder devices in a multi-stage system20 be of substantially similar size, the larger (lower-pressure)cylinder devices may be divided up into two or more smaller cylinderdevices communicating in parallel. An example of such a stage isillustrated in FIG. 7, which is an alternative embodiment of the stageof embodiment of FIG. 4. In this configuration, four substantiallysimilar cylinder devices 21 b 1-21 b 4 share a single pressure cell 25 bcontaining body of liquid 49 b. However, if it is desirable to operatethe cylinder devices out of phase with each other so that the system asa whole may convey power more uniformly, separate pressure cells will berequired for each cylinder device. As mentioned above, the exception iscylinder devices that are 180 degrees out of phase, which then may sharea common pressure cell.

Referring back to the embodiment of FIG. 7, each cylinder device 21 b1-21 b 4 operates according to the scheme used for the mist-type systemdescribed in the Single-Stage System section above.

Multi-cylinder device stages may be single or double-acting, and may useeither liquid mist or bubbles to effect heat exchange. A multi-stagesystem may have some stages with a single cylinder device and otherswith multiple cylinder devices.

Options for Conveying Mechanical Power To and From the System

At least four methods may be applied to convey power to and from a stagein accordance with the present invention. These are described asfollows, and illustrated in FIG. 8.

W. A direct-acting hydraulic cylinder device 21 w is shown and operatesas follows. During the expansion cycle, air entering the chamber 22 w ofcylinder device 21 w, via valve 121 w and pipe 122 w, urges thehydraulic liquid 49 w out through valve 123 w. It then flows throughpipe 124 w. The force thus pneumatically applied against the liquid canbe used to operate a hydraulic device (e.g., a hydraulic motor 57, ahydraulic cylinder device or a hydro turbine as shown in FIG. 9) tocreate mechanical power. During the compression cycle, the reverseprocess occurs. An external source of mechanical power operates ahydraulic pump or cylinder device, which forces hydraulic liquid 49 winto the cylinder chamber 22 w, through valve 123 w, compressing the airin the chamber. When the air has reached the desired pressure, valve 121w is opened, allowing the compressed air to flow from the cylinderchamber 22 w to the next higher-pressure stage or to the air tank.

X. A single-acting piston 23 x (also illustrated in FIG. 4) may beconnected to a conventional crankshaft via a piston rod 19 x. Itsoperation is described in detail in the section titled Single-StageSystem above.

Y. A double-acting piston (also illustrated in FIG. 5), may similarly beconnected to a crankshaft via a piston rod 19 y. Its operation isdescribed in detail in the section titled Multiple Phases above.

Z. A hydraulic cylinder device 21 with a diaphragm 125 is illustratedsuch that when air enters the cylinder chamber 22 z, via valve 121 z,during the expansion cycle, the diaphragm 125 is forced downwardly.Consequently, the hydraulic liquid 49 z is urged or driven through valve123 z and through pipe 124 z. Similarly, during compression, thehydraulic liquid 49 z is driven through valve 123 z and into thecylinder chamber 22 z, deflecting the diaphragm 125 upwardly,compressing the air in the upper part of the chamber 22 z, which thenexits via valve 121 z.

Note that all four of these options can be used with either the liquidmist technique or the bubbles technique to effect heat transfer. Thenecessary valves and nozzles to supply the mist or bubbles are not shownon FIG. 8.

While the above examples describe the use of pistons, other types ofmoveable elements may be utilized and still remain within the scope ofthe present invention. Examples of alternative types of apparatuseswhich could be utilized include but are not limited to screwcompressors, multi-lobe blowers, vane compressors, gerotors, andquasi-turbines.

Single-Stage, Single-Acting Energy Storage System:

Referring now to the embodiment of FIG. 3, a single-stage, single-actingenergy storage system 20 is illustrated that utilizes two pressure cells25 d and 25 e configured as direct-acting hydraulic cylinder devices(option A above). The two pressure cells operate substantially 180degrees out of phase with each other. Liquid mist is used to effect heatexchange during the compression cycle, and both bubbles and mist areused to effect heat exchange during the expansion cycle.

As described above in connection with FIG. 1, the apparatus of FIG. 3further includes a controller/processor 3006 in electronic communicationwith a computer-readable storage device 3008, which may be of anydesign, including but not limited to those based on semiconductorprinciples, or magnetic or optical storage principles. Controller 3006is shown as being in electronic communication with a universe of activeelements in the system, including but not limited to valves, pumps,chambers, nozzles, and sensors. Specific examples of sensors utilized bythe system include but are not limited to pressure sensors (P) 3016,3022, and 3038, temperature sensors (T) 3018, 3024, and 3040, humiditysensor (H) 3010, and volume sensors (V) 3036, 3014, and 3020.

The compression cycle of the single-stage, single-acting energy storagesystem 20 proceeds as follows:

Step 1 2 3 4 Description Compress air in Move Compress air in Move cell25d while compressed air cell 25e while compressed air spraying mist,from cell 25d to spraying mist, from cell 25e to and replenish the airtank and replenish the air tank air in cell 25e air in cell 25d Valve130 Closed Closed Open Open Valve 131 Open Open Closed Closed Valve 132Closed Open Closed Closed Valve 133 Closed Closed Closed Closed Valve134 Open Open Closed Closed Valve 135 Closed Closed Open Open Valve 136Closed Closed Closed Open Valve 137 Closed Closed Closed Closed Valve138 Pump out to cell Pump out to Pump out to cell Pump out to cell 25d,pump in cell25d, pump 25e, pump in 25e, pump in from cell 25e in fromcell 25e from cell 25d from cell 25d Pump 46 On On On On

During step 1, fluid is pumped from pressure cell 25 e using thehydraulic pump-motor 57 into pressure cell 25 d, thereby compressing theair inside cell 25 d. Fluid mist is sprayed through nozzle 141, whichabsorbs the heat of compression. When the pressure inside cell 25 d hasreached the pressure of the air tank 32, valve 132 is opened to let thecompressed air move to the air tank. As these steps have beenprogressing, air at atmospheric pressure has entered the system via pipe10 and air filter 26 d and thence into cell 25 e to replace the fluidpumped out of it.

When all the air has been driven out of cell 25 d, the process reverses,and step 3 commences, with the four-way valve 138 changing state tocause liquid to be pumped out of cell 25 d and into cell 25 e, causingthe air in cell 25 e to be compressed. Thus, liquid is pumped back andforth between cells 25 d and 25 e in a continuous cycle.

The expansion cycle of the single-stage, single-acting energy storagesystem proceeds as follows:

In step 1, compressed air is bubbled into pressure cell 25 d via nozzle11 d. As the bubbles rise, they exchange heat with the body of fluid 49d. Air is forced out of cell 25 d, passing through pipe 139 d, and thendriving hydraulic motor 57, thereby delivering mechanical power

In step 2, the valve 133 admitting the compressed air into cell 25 d isclosed, allowing the air in cell 25 d to expand, continuing to operatemotor 57. In step 3, once the air admitted in step 1 has risen to thetop of cell 25 d and can no longer exchange heat with the body of fluid49 d, fluid mist is sprayed into the cell via nozzle 141 to further warmthe expanding air.

As fluid passes through the hydraulic motor 57 during steps 1, 2, and 3,it continues through pipe 139 e and enters pressure cell 25 e, urgingthe air present in that cell through pipe 140 and into the liquidtrap-reservoir 13 d, and thence into the atmosphere via air filter 26 dand finally pipe 10.

Steps 4, 5, and 6 mirror steps 1, 2, and 3. That is, compressed air isbubbled into pressure cell 25 e, forcing fluid through the hydraulicmotor 57, and then into pressure cell 25 d.

If reservoir 13 e is depleted during operation, excess liquid is pumpedfrom the bottom of reservoir 13 d into cells 25 d and 25 e, using apump, not shown in the figure, connected to pipe 140.

Over time, both liquid traps 13 d and 13 e will change temperature dueto the air and entrained droplets transferring heat—a heat exchanger, asshown by coils 52 d and 52 e, in pressure cells 25 d and 25 e, andconnected to a conventional external heat exchanger 12 that exchangesheat with the environment, will moderate the temperature to nearambient.

The volume of compressed air bubbled into the cells during steps 1 and 3depends on the power output desired. If the air can expand fully to oneatmosphere without displacing all the liquid in the cell, then themaximum amount of work will be done during the stroke. If the air doesnot fully expand during the stroke, all else being equal the poweroutput will be higher at the expense of efficiency.

Note that the pressure cells cannot be of insufficient height so thatthe air bubbles reach the surface of the liquid during the course of thestroke, since almost all heat exchange with the body of liquid occurswhile the bubbles are rising through it. However, they must besufficiently tall for the column of bubbles to completely separate fromthe fluid by the time the exhaust stroke completes. If the system mustbe run slowly, some of the bubbles will reach the top before expansioncompletes. In this event, liquid mist is sprayed through nozzles 141 (instep 3) or 142 (in step 6) of the expansion cycle.

FIG. 3 is meant to illustrate the basic principles. In a system in whicha large expansion ratio is desired will require the use of multiplestages 24.

System Configurations

It will be understood that a plurality of energy storage systemembodiments, designed in accordance with this invention, are possible.These energy storage system 20 may be single or multi-stage. Stages maybe single-cylinder device or multi-cylinder device. Heat exchange may beeffected via liquid mist or via bubbles. Power may be conveyed in andout of the system via any of the at least four methods described in theprevious section. Each possible configuration has advantages for aspecific application or set of design priorities. It would not bepracticable to describe every one of these configurations here, but itis intended that the information given should be sufficient for onepracticed in the art to configure any of these possible energy storagesystems as required.

All of the many possible configurations have three elements in common:

1. Near-isothermal expansion and compression of air, with the requiredheat exchange effected by a liquid phase in high-surface-area contactwith the air.

2. A reversible mechanism capable of both compression and expansion ofair.

3. Electronic control of valve timing so as to obtain the highestpossible work output from a given volume of compressed air.

Note that all the configurations described herein use and generate powerin mechanical form, be it hydraulic pressure or the reciprocating actionof a piston. In most applications, however, the requirement will be forthe storage of electrical energy. In that case, a generator, along withappropriate power conditioning electronics, must be added to convert themechanical power supplied by the system during expansion to electricalpower. Similarly, the mechanical power required by the system duringcompression must be supplied by a motor. Since compression and expansionare never done simultaneously, a motor-generator may be used to performboth functions. If the energy storage system utilizes a hydraulic motoror a hydro turbine, then the shaft of that device connects directly orvia a gearbox to the motor-generator. If the energy storage systemutilizes reciprocating pistons, then a crankshaft or other mechanicallinkage that can convert reciprocating motion to shaft torque isrequired.

Use of Waste Heat During Expansion

In order to operate isothermally, the tendency of air to cool as itexpands while doing work (i.e. by pushing a piston or displacinghydraulic liquid) must be counteracted by heat exchange with the ambientair or with a body of water (e.g. a stream or lake). If, however, someother source of heat is available—for example, hot water from a steamcondenser—it may be used advantageously during the expansion cycle. InFIG. 1, as described in the Single-Stage System section above, pipes 53and 54 lead to an external heat exchanger. If those pipes are routedinstead to a heat source, the efficiency of the expansion process can beincreased dramatically.

Because the system operates substantially at or near ambienttemperature, the source of heat need only be a few degrees above ambientin order to be useful in this regard. The heat source must, however,have sufficient thermal mass to supply all the heat required to keep theexpansion process at or above ambient temperature throughout the cycle.

As described in detail above, embodiments of systems and methods forstoring and recovering energy according to the present invention areparticularly suited for implementation in conjunction with a hostcomputer including a processor and a computer-readable storage medium.Such a processor and computer-readable storage medium may be embedded inthe apparatus, and/or may be controlled or monitored through externalinput/output devices. FIG. 20 is a simplified diagram of a computingdevice for processing information according to an embodiment of thepresent invention. This diagram is merely an example, which should notlimit the scope of the claims herein. One of ordinary skill in the artwould recognize many other variations, modifications, and alternatives.Embodiments according to the present invention can be implemented in asingle application program such as a browser, or can be implemented asmultiple programs in a distributed computing environment, such as aworkstation, personal computer or a remote terminal in a client serverrelationship.

FIG. 20 shows computer system 2010 including display device 2020,display screen 2030, cabinet 2040, keyboard 2050, and mouse 2070. Mouse2070 and keyboard 2050 are representative “user input devices.” Mouse2070 includes buttons 2080 for selection of buttons on a graphical userinterface device. Other examples of user input devices are a touchscreen, light pen, track ball, data glove, microphone, and so forth.FIG. 20 is representative of but one type of system for embodying thepresent invention. It will be readily apparent to one of ordinary skillin the art that many system types and configurations are suitable foruse in conjunction with the present invention. In a preferredembodiment, computer system 2110 includes a Pentium™ class basedcomputer, running Windows™ XP™ or Windows 7™ operating system byMicrosoft Corporation. However, the apparatus is easily adapted to otheroperating systems and architectures by those of ordinary skill in theart without departing from the scope of the present invention.

As noted, mouse 2170 can have one or more buttons such as buttons 2180.Cabinet 2140 houses familiar computer components such as disk drives, aprocessor, storage device, etc. Storage devices include, but are notlimited to, disk drives, magnetic tape, solid-state memory, bubblememory, etc. Cabinet 2140 can include additional hardware such asinput/output (I/O) interface cards for connecting computer system 2110to external devices external storage, other computers or additionalperipherals, further described below.

FIG. 20A is an illustration of basic subsystems in computer system 2010of FIG. 20. This diagram is merely an illustration and should not limitthe scope of the claims herein. One of ordinary skill in the art willrecognize other variations, modifications, and alternatives. In certainembodiments, the subsystems are interconnected via a system bus 2075.Additional subsystems such as a printer 2074, keyboard 2078, fixed disk2079, monitor 2076, which is coupled to display adapter 2082, and othersare shown. Peripherals and input/output (I/O) devices, which couple toI/O controller 2071, can be connected to the computer system by anynumber of approaches known in the art, such as serial port 2077. Forexample, serial port 2077 can be used to connect the computer system toa modem 2081, which in turn connects to a wide area network such as theInternet, a mouse input device, or a scanner. The interconnection viasystem bus allows central processor 2073 to communicate with eachsubsystem and to control the execution of instructions from systemmemory 2072 or the fixed disk 2079, as well as the exchange ofinformation between subsystems. Other arrangements of subsystems andinterconnections are readily achievable by those of ordinary skill inthe art. System memory, and the fixed disk are examples of tangiblemedia for storage of computer programs, other types of tangible mediainclude floppy disks, removable hard disks, optical storage media suchas CD-ROMS and bar codes, and semiconductor memories such as flashmemory, read-only-memories (ROM), and battery backed memory.

FIG. 21 is a schematic diagram showing the relationship between theprocessor/controller, and the various inputs received, functionsperformed, and outputs produced by the processor controller. Asindicated, the processor may control various operational properties ofthe apparatus, based upon one or more inputs.

An example of such an operational parameter that may be controlled isthe timing of opening and closing of a valve allowing the inlet of airto the cylinder during an expansion cycle. FIGS. 11A-C is a simplifiedand enlarged view of the cylinder 22 of the single-stage system of FIG.1, undergoing an expansion cycle as described previously.

Specifically, during step 2 of the expansion cycle, a pre-determinedamount of air V₀, is added to the chamber from the pressure cell, byopening valve 37 for a controlled interval of time. This amount of airV₀ is calculated such that when the piston reaches the end of theexpansion stroke, a desired pressure within the chamber will beachieved.

In certain cases, this desired pressure will approximately equal that ofthe next lower pressure stage, or atmospheric pressure if the stage isthe lowest pressure stage or is the only stage. Thus at the end of theexpansion stroke, the energy in the initial air volume V₀ has been fullyexpended, and little or no energy is wasted in moving that expanded airto the next lower pressure stage.

To achieve this goal, valve 37 is opened only for so long as to allowthe desired amount of air (V₀) to enter the chamber, and thereafter insteps 3-4 (FIGS. 11B-C), valve 37 is maintained closed. In certainembodiments, the desired pressure within the chamber may be within 1psi, within 5 psi, within 10 psi, or within 20 psi of the pressure ofthe next lower stage.

In other embodiments, the controller/processor may control valve 37 tocause it to admit an initial volume of air that is greater than V₀. Suchinstructions may be given, for example, when greater power is desiredfrom a given expansion cycle, at the expense of efficiency of energyrecovery.

Timing of opening and closing of valves may also be carefully controlledduring compression. For example, as shown in FIGS. 11D-E, in the steps 2and 3 of the table corresponding to the addition of mist andcompression, the valve 38 between the cylinder device and the pressurecell remains closed, and pressure builds up within the cylinder.

In conventional compressor apparatuses, accumulated compressed air iscontained within the vessel by a check valve, that is designed tomechanically open in response to a threshold pressure. Such use of theenergy of the compressed air to actuate a check valve, detracts from theefficiency of recovery of energy from the air for performing usefulwork.

By contrast, as shown in FIG. 11F, embodiments of the present inventionmay utilize the controller/processor to precisely open valve 38 underthe desired conditions, for example where the built-up pressure in thecylinder exceeds the pressure in the pressure cell by a certain amount.In this manner, energy from the compressed air within the cylinder isnot consumed by the valve opening process, and efficiency of energyrecovery is enhanced. Embodiments of valve types that may be subject tocontrol to allow compressed air to flow out of a cylinder include butare not limited to pilot valves, cam-operated poppet valves, rotaryvalves, hydraulically actuated valves, and electronically actuatedvalves.

While the timing of operation of valves 37 and 38 of the single stageapparatus may be controlled as described above, it should be appreciatedthat valves in other embodiments may be similarly controlled. Examplesof such valves include but are not limited to valves 130, 132, 133, 134,136, and 137 of FIG. 3, valves 37 b and 38 b of FIG. 4, valves 37 b 1,38 b 1, 37 b 2 and 38 b 2 of FIG. 5, valves 106 c and 114 c of FIG. 6,and the valves 37 b 1-4 and 38 b 1-4 that are shown in FIG. 7.

Another example of a system parameter that can be controlled by theprocessor, is the amount of liquid introduced into the chamber. Basedupon one or more values such as pressure, humidity, calculatedefficiency, and others, an amount of liquid that is introduced into thechamber during compression or expansion, can be carefully controlled tomaintain efficiency of operation. For example, where an amount of airgreater than V₀ is inlet into the chamber during an expansion cycle,additional liquid may need to be introduced in order to maintain thetemperature of that expanding air within a desired temperature range.

The present invention is not limited to those particular embodimentsdescribed above. Other methods and apparatuses may fall within the scopeof the invention. For example, the step of adding liquid to a cylinderdevice is not required during every cycle. In addition, liquid may beadded to the chamber at the same time air is being inlet.

Accordingly, the following table describes steps in an embodiment of acompression cycle for a single-stage system utilizing liquid mist toeffect heat exchange, as shown in connection with FIGS. 12A-C, wheresimilar elements as in FIG. 1 are shown:

Step 1 2 3 Description Refill cylinder device Compress Move compressedair to pressure cell Valve 35 Closed Closed Closed Valve 36 Open ClosedClosed Valve 37 Closed Closed Closed Valve 38 Closed Closed Open Valve39 Open Closed Closed Valve 40 Closed Closed Closed Valve 41 Open OpenOpen Valve 42 Closed Closed Closed Valve 43 Open Closed Closed Pump 46Off Off Off Pump 47 On Off Off Piston 23 At TDC at start of At BDC atBetween step start of step BDC and TDC

The corresponding expansion cycle where liquid is introduced at the sametime as air, is shown in the table below, in connection with FIGS.13A-C:

Step 1 2 3 Description Add compressed air and Expansion Exhaust spentair liquid mist to cylinder device Valve 35 Closed Closed Closed Valve36 Closed Closed Open Valve 37 Open Closed Closed Valve 38 Closed ClosedClosed Valve 39 Open Closed Closed Valve 40 Open Open Open Valve 41Closed Closed Closed Valve 42 Closed Closed Open Valve 43 Closed ClosedClosed Pump 46 Off Off Off Pump 47 On Off Off Piston 23 At TDC at startof step Near TDC at At BDC at start start of step of step

Moreover, where bubbles are utilized to effect heat exchange, the stepof replenishing liquid is not required in every cycle. The followingtable, in conjunction with FIGS. 14A-C, describes steps in an embodimentof a compression cycle for a single-stage system utilizing bubbles toeffect heat exchange, where elements similar to those in FIG. 6 arereferenced:

Step 1 2 3 Description Fill cylinder device Compress Transfer air topressure with air cell Valve 108c Closed Closed Closed Valve 109c ClosedClosed Open Valve 114c Closed Closed Closed Valve 41c Open Open OpenValve 40c Closed Closed Closed Valve 106c Open Closed Closed Valve 110cClosed Closed Closed Valve 111c Closed Closed Closed Pump 105c On OffOff Pump 113c Off Off Off Piston 23c At top of liquid at At TDC at NearBDC at start of start of step start of step step

The corresponding expansion cycle for this system is shown in the tablebelow in conjunction with FIGS. 15A-C:

Step 1 2 3 Description Add compressed air to Expansion Exhaust spent aircylinder device Valve 108c Closed Closed Open Valve 109c Closed ClosedClosed Valve 114c Open Closed Closed Valve 41c Closed Closed ClosedValve 40c Open Open Open Valve 106c Closed Closed Closed Valve 110cClosed Closed Closed Valve 111c Closed Closed Closed Pump 105c Off OffOff Pump 113c Off Off Off Piston 23c At top of liquid Near top of At TDCat start liquid

Shown in FIGS. 16A-D and in the table below, are the steps of anembodiment of a compression cycle for a multi-phase stage, referencingthe elements of FIG. 5:

Step 1 2 3 4 Description Add mist Continue, Add mist and air Continue,and air to moving air to to chamber 22b2 moving air chamber pressurecell and compress air to 22b1 and in chamber 22b1 pressure compress cellair in chamber 22b2 Valve 35b1 Open Open Closed Closed Valve 36b1 ClosedClosed Closed Closed Valve 37b1 Closed Closed Closed Closed Valve 38b1Closed Closed Closed Open Valve 39b1 Open Open Closed Closed Valve 35b2Closed Closed Open Open Valve 36b2 Closed Closed Closed Closed Valve37b2 Closed Closed Closed Closed Valve 38b2 Closed Open Closed ClosedValve 39b2 Closed Closed Open Open Valve 40b Closed Closed Closed ClosedValve 41b Open Open Open Open Pump 47b On On On On Piston 23b TDC atBetween TDC BDC at start of Between start of and BDC, step BDC and stepmoving down TDC, moving up

The corresponding expansion cycle for the double-acting stage isillustrated in FIGS. 17A-D and in the following table:

Step 1 2 3 4 Description Add mist Allow air in Add mist Allow air in andair to chamber 22b1 and air to chamber 22b2 chamber to expand andchamber to expand and 22b1 and continue 22b2 and continue exhaust airexhausting air exhaust air exhausting air from from chamber from fromchamber chamber 22b2 chamber 22b1 22b2 22b1 Valve 35b1 Closed ClosedOpen Open Valve 36b1 Closed Closed Closed Closed Valve 37b1 Open ClosedClosed Closed Valve 38b1 Closed Closed Closed Closed Valve 39b1 OpenClosed Closed Closed Valve 35b2 Open Open Closed Closed Valve 36b2Closed Closed Closed Closed Valve 37b2 Closed Closed Open Closed Valve38b2 Closed Closed Closed Closed Valve 39b2 Closed Closed Open ClosedValve 40b Open Open Open Open Valve 41b Closed Closed Closed Closed Pump47b On Off On Off Piston 23b TDC at Between TDC BDC at start Between BDCstart of and BDC, of step and TDC, step moving down moving up

A compression cycle for a single-stage, single-acting energy storagesystem shown in FIGS. 18A-D, is described in the table below, with mistsprayed at the time of inlet of air into the cylinder, with similarelements as shown in FIG. 3:

Step 1 2 3 4 Description Compress air Move Compress air Move in cell 25dcompressed in cell 25e com- while spraying air from cell while sprayingpressed mist, and 25d to air mist, and air from replenish the tankreplenish the cell 25e to air in cell 25e air in cell 25d air tank Valve130 Closed Closed Open Open Valve 131 Closed Closed Open Open Valve 132Closed Open Closed Closed Valve 133 Closed Closed Closed Closed Valve134 Open Open Closed Closed Valve 135 Open Open Closed Closed Valve 136Closed Closed Closed Open Valve 137 Closed Closed Closed Closed Valve138 Fluid out from Fluid out Fluid out from Fluid out cell 25e, in tofrom cell cell 25d, in to from cell cell 25d 25e, in to cell 25e 25d, into cell 25d cell 25e Pump 46 On On On On

The corresponding expansion cycle of the single-stage, single-actingenergy storage system proceeds as follows as shown in FIGS. 19A-D:

Step 1 2 3 4 De- Add air to cell Expand air in Add air to cell Expandscription 25d while cell 25d while 25e while air in cell spraying mist,spraying mist, spraying mist, 25e while and move air continue to andmove air spraying from cell 25e exhaust cell from cell 25d mist, 25econtinue to exhaust cell 25d Valve 130 Closed Closed Open Open Valve 131Open Open Closed Closed Valve 132 Closed Closed Closed Closed Valve 133Open Closed Closed Closed Valve 134 Open Open Closed Closed Valve 135Closed Closed Open Open Valve 136 Closed Closed Closed Closed Valve 137Closed Closed Open Closed Valve 138 Fluid out from Fluid out from Fluidout from Fluid out cell 25d, in to cell 25d, in to cell 25e, in to fromcell cell 25e cell 25e cell 25d 25e, in to cell 25d Pump 46 On On On On

Variations on the specific embodiments describe above, are possible. Forexample, in some embodiments, a plurality of pistons may be incommunication with a common chamber. In other embodiments, a multistageapparatus may not include a separate pressure cell.

For example, in the embodiment of FIG. 10, the stages are connecteddirectly together through a heat exchanger, rather than through apressure cell as in the embodiment of FIG. 4. The relative phases of thecycles in the two stages must be carefully controlled so that when Stage1 is performing an exhaust step, Stage 2 is performing an intake step(during compression). When Stage 2 is performing an exhaust step, Stage1 is performing an intake step (during expansion).

The timing is controlled so the pressures on either side of heatexchanger 10024 are substantially the same when valves 37 and 10058 areopen. Liquid for spray nozzle 44 is supplied from an excess water incylinder 22 by opening valve 10036 and turning on pump 10032. Similarly,liquid for spray nozzle 10064 is supplied from an excess water incylinder 10046 by opening valve 10038 and turning on pump 10034. Suchprecise timing during operation may be achieved with the operation of acontroller/processor that is communication with a plurality of thesystem elements, as has been previously described.

The present invention is not limited to the embodiments specificallydescribed above. For example, while water has been described as theliquid that is injected into air as a mist, other liquids could beutilized and fall within the scope of the present invention. Examples ofliquids that could be used include polypropylene glycol, polyethyleneglycol, and alcohols.

The following claims relate to compression.

1. A method for storing energy, the method comprising:

-   -   introducing a first quantity of air at a first temperature into        a first chamber;    -   in a compression cycle, subjecting the first quantity of air to        compression by a first piston coupled to the first chamber;    -   injecting a first determined quantity of fluid into the first        quantity of air to absorb thermal energy generated by the        compression cycle and thereby maintain the first quantity of air        in a first temperature range during the compression; and    -   transferring at least a portion of the first quantity of air to        a first pressure cell.

2. The method of claim 1 wherein the first determined quantity of fluidis based upon one or more control parameters.

3. The method of claim 2 wherein the control parameter is calculated forthe compression cycle from a measured physical property.

4. The method of claim 2 wherein the control parameter comprises amaximum increase in a temperature of the first quantity of air duringcompression.

5. The method of claim 2 wherein the control parameter comprises anamount of the fluid present in liquid form inside the chamber.

6. The method of claim 2 wherein the control parameter comprises anefficiency.

7. The method of claim 2 wherein the control parameter comprises a powerinput to the piston.

8. The method of claim 2 wherein the control parameter comprises a speedof the piston.

9. The method of claim 2 wherein the control parameter comprises a forceon the piston.

10. The method of claim 1 wherein the piston is solid, liquid, or acombination of solid and liquid.

11. The method of claim 1 wherein the first temperature range isreflected by a change in a temperature of the first quantity of air froma first temperature to a second temperature below a boiling point of thefluid.

12. The method of claim 11 wherein the fluid comprises water.

13. The method of claim 12 wherein the first temperature range is about60 degrees Celsius or less.

14. The method of claim 1 wherein the first determined quantity of fluidis injected by spraying or misting.

15. The method of claim 1 wherein the thermal energy transferred fromthe first quantity of air to the first determined quantity of fluid isfacilitated by bubbling air through a liquid.

16. The method of claim 1 further comprising transferring compressed airwithin the pressure cell to a storage tank.

The following claims relate to compression and expansion.

17. The method of claim 1 further comprising:

-   -   in an expansion cycle, transferring a second quantity of air        from the first pressure cell to the first chamber;    -   allowing the second quantity of air to expand and drive the        first piston; and    -   injecting a second determined quantity of fluid into the second        quantity of air to provide thermal energy absorbed by the        expanding air and thereby maintain the second quantity of air in        a second temperature range during the expansion.

18. The method of claim 17 further comprising generating electricalpower from the driving of the first piston.

19. The method of claim 17 wherein the second determined quantity offluid is based upon a one or more control parameters.

20. The method of claim 17 wherein the control parameter is calculatedfor the expansion cycle from a measured physical property.

21. The method of claim 17 wherein the control parameter comprises amaximum decrease in a temperature of the second quantity of air duringthe expansion.

22. The method of claim 17 wherein the control parameter comprises anamount of the fluid present in liquid form inside the chamber.

23. The method of claim 17 wherein the control parameter comprises anefficiency.

24. The method of claim 17 wherein the control parameter comprises apower output by the first piston.

25. The method of claim 17 wherein the control parameter comprises aspeed of the piston.

26. The method of claim 17 wherein the control parameter comprises aforce on the piston.

27. The method of claim 17 wherein the first determined quantity offluid is injected by spraying or misting.

28. The method of claim 17 wherein thermal energy is transferred fromthe second quantity of air to the second determined quantity of fluidfacilitated by bubbling air through a liquid.

29. The method of claim 17 wherein the fluid comprises water.

30. The method of claim 17 further comprising placing the chamber incommunication with additional thermal energy during the expansion cycle.

31. The method of claim 30 wherein the additional thermal energy iswaste heat from another thermal source.

32. The method of claim 17 wherein the second temperature range isreflected by a change in a temperature of the second quantity of airfrom a first temperature to a second temperature above a freezing pointof the fluid.

33. The method of claim 32 wherein the fluid comprises water.

34. The method of claim 33 wherein the second temperature range is about11 degrees Celsius or less.

34a. The method of claim 17 wherein at an end of an expansion stroke ofthe first piston, the second quantity of air is configured to produce apressure on the first piston substantially equal to a desired pressure.

34b. The method of claim 34a, wherein the desired pressure is an inputpressure of the next lowest pressure stage, or is ambient pressure.

34c. The method of claim 34a wherein the desired pressure is calculatedto maximize an efficiency of expansion.

34d. The method of claim 34a wherein the desired pressure is calculatedto produce a desired level of power output.

34e. The method of claim 34a wherein the desired pressure is withinapproximately 5 psi of an input pressure of the next lowest pressurestage.

The following claims relate to multi-stage operation.

35. The method of claim 17 further comprising:

-   -   providing a second chamber in selective fluid communication with        the first pressure cell and with a second pressure cell;    -   introducing from the first pressure cell, a third quantity of        air at a second temperature into the second chamber;    -   in a compression cycle of the second chamber,    -   subjecting the third quantity of air to compression by a second        piston coupled to the second chamber;    -   injecting a third determined quantity of fluid into the third        quantity of air to absorb thermal energy generated by the        compression and thereby maintain the third quantity of air in a        third temperature range during the compression; and    -   transferring at least a portion of the third quantity of air to        the second pressure cell.

36. The method of claim 35 further comprising:

-   -   in an expansion cycle of the second chamber, transferring a        fourth quantity of air from the second pressure cell to the        second chamber;    -   allowing the fourth quantity of air to expand and drive the        second piston;    -   injecting a fourth determined quantity of fluid into the fourth        quantity of air to provide thermal energy absorbed by the        expanding air and thereby maintain the fourth quantity of air in        a fourth temperature range during the expansion; and    -   transferring at least a portion of the fourth quantity of air        from the second chamber to the first pressure cell.

The following claims relate to expansion.

37. A method for releasing stored energy, the method comprising:

-   -   in an expansion cycle, transferring a quantity of air from a        pressure cell to a chamber having a piston disposed therein;    -   allowing the quantity of air to expand and drive the piston; and    -   injecting a determined quantity of fluid into the quantity of        air to provide thermal energy absorbed by the expanding air and        thereby maintain the quantity of air in a first temperature        range during the expansion.

38. The method of claim 37 wherein the determined quantity of fluid isbased upon one or more control parameters.

39. The method of claim 38 wherein the control parameter is calculatedfrom a measured physical property.

40. The method of claim 38 wherein the control parameter comprises amaximum decrease in a temperature of the quantity of air during theexpansion.

41. The method of claim 38 wherein the control parameter comprises anamount of the fluid present in liquid form inside the chamber.

42. The method of claim 38 wherein the control parameter comprises anefficiency.

43. The method of claim 38 wherein the control parameter comprises apower input to the piston.

44. The method of claim 38 wherein the control parameter comprises aspeed of the piston.

45. The method of claim 38 wherein the control parameter comprises aforce of the piston.

46. The method of claim 38 wherein the piston is solid, liquid, or acombination of solid and liquid.

47. The method of claim 38 wherein the fluid comprises water.

48. The method of claim 38 wherein the first temperature range isreflected by a change in a temperature of the first quantity of air froma first temperature to a second temperature, the change less than adetermined value.

49. The method of claim 48 wherein the lower temperature is greater thana freezing point of the fluid.

50. The method of claim 48 wherein the higher temperature is less than aboiling point of the fluid.

51. The method of claim 38 wherein the first determined quantity offluid is injected by spraying or misting.

52. The method of claim 38 wherein the thermal energy transferred fromthe quantity of air to the determined quantity of fluid is facilitatedby bubbling air through a liquid.

52a. The method of claim 37 wherein at an end of an expansion stroke ofthe piston, the quantity of air is configured to produce a pressure onthe piston substantially equal to a desired pressure.

52b. The method of claim 37, wherein the desired pressure is an inputpressure of the next lowest pressure stage, or is ambient pressure.

52c. The method of claim 37 wherein the desired pressure is calculatedto maximize an efficiency of expansion.

52d. The method of claim 37 wherein the desired pressure is calculatedto produce a desired level of power output.

52e. The method of claim 37 wherein the desired pressure is withinapproximately 5 psi of an input pressure of the next lowest pressurestage.

The following claims relate to temperature difference during systemoperation.

53. A method comprising:

-   -   providing an energy storage system comprising a pressure cell in        selective fluid communication with a chamber having a moveable        piston disposed therein;    -   flowing air into the chamber;    -   in a compression cycle, storing energy by placing the piston in        communication with an energy source to compress the air within        the chamber, and then transferring the compressed air to the        pressure cell; and then    -   in an expansion cycle, releasing energy by transferring air from        the pressure cell back into the chamber while allowing the        piston to move in response to expansion of air inside the        chamber;    -   monitoring an operational parameter of the compression cycle        and/or the expansion cycle; and    -   controlling the operational parameter to maintain a temperature        of air in the chamber within a range.

54. The method of claim 53 wherein determining an operational parametercomprises controlling an amount of a liquid introduced into the airwithin the chamber during the compression cycle.

55. The method of claim 53 wherein the liquid comprises water.

56. The method of claim 53 wherein determining an operational parametercomprises controlling an amount of a liquid introduced into the airwithin the chamber during the expansion cycle.

57. The method of claim 56 wherein the liquid comprises water.

58. The method of claim 53 wherein a lower bound of the range is greaterthan a freezing point of a liquid introduced into the air within thechamber.

59. The method of claim 58 wherein the liquid comprises water.

60. The method of claim 53 wherein an upper bound of the range is lowerthan a boiling point of a liquid introduced into the air within thechamber.

61. The method of claim 60 wherein the liquid comprises water.

62. The method of claim 53 wherein determining an operational parametercomprises controlling a timing of the transfer of air from the pressurecell into the chamber during the expansion cycle.

62a. The method of claim 62 wherein the timing is controlled such thatat an end of an expansion stroke of the piston, the transferred air isconfigured to produce a desired pressure on the piston.

62b. The method of claim 62a, wherein the desired pressure is an inputpressure of the next lowest pressure stage, or is ambient pressure.

62c. The method of claim 62a wherein the desired pressure is calculatedto maximize an efficiency of expansion.

62d. The method of claim 62a wherein the desired pressure is calculatedto produce a desired level of power output.

62e. The method of claim 62a wherein the desired pressure is withinapproximately 5 psi of an input pressure of the next lowest pressurestage.

63. The method of claim 53 wherein determining an operational parametercomprises monitoring a pressure in the pressure cell.

64. The method of claim 53 wherein determining an operational parametercomprises monitoring a pressure in the chamber.

65. The method of claim 53 wherein determining an operational parametercomprises monitoring a temperature of the air in the chamber.

66. The method of claim 53 wherein determining an operational parametercomprises monitoring a humidity of the air flowed into the chamber.

67. The method of claim 53 wherein determining an operational parametercomprises monitoring a humidity of air exhausted from the chamber.

68. The method of claim 53 wherein determining an operational parametercomprises monitoring a power released during the expansion cycle.

69. The method of claim 53 wherein determining an operational parametercomprises monitoring a position of the piston.

70. The method of claim 53 wherein determining an operational parametercomprises monitoring a force on the piston.

71. The method of claim 54 wherein determining an operational parametercomprises monitoring a temperature of the liquid.

72. The method of claim 56 wherein determining an operational parametercomprises monitoring a temperature of the liquid.

73. The method of claim 54 wherein determining an operational parametercomprises monitoring a rate of flow of the liquid.

74. The method of claim 56 wherein determining an operational parametercomprises monitoring a rate of flow of the liquid.

75. The method of claim 54 wherein determining an operational parametercomprises monitoring a level of the liquid in the chamber.

76. The method of claim 56 wherein determining an operational parametercomprises monitoring a level of the liquid in the chamber.

77. The method of claim 54 wherein determining an operational parametercomprises monitoring a volume of the liquid in the chamber.

78. The method of claim 56 wherein determining an operational parametercomprises monitoring a volume of the liquid in the chamber.

79. The method of claim 53 wherein:

-   -   the piston is in communication with a rotating shaft; and    -   determining an operational parameter comprises monitoring a        speed of the rotating shaft.

80. The method of claim 53 wherein:

-   -   the piston is in communication with a rotating shaft; and    -   determining an operational parameter comprises monitoring a        torque of the rotating shaft.

81. The method of claim 53 wherein the operational parameter iscontrolled based upon a derived parameter calculated from the monitoredoperational parameter.

82. The method of claim 81 wherein the derived parameter is selectedfrom the group comprising, an efficiency of power conversion, anexpected power output, an expected output speed of a rotating shaft incommunication with the piston, an expected output torque of a rotatingshaft in communication with the piston, an expected input speed of arotating shaft in communication with the piston, an expected inputtorque of a rotating shaft in communication with the piston, a maximumoutput speed of a rotating shaft in communication with the piston, amaximum output torque of a rotating shaft in communication with thepiston, a minimum output speed of a rotating shaft in communication withthe piston, a minimum output torque of a rotating shaft in communicationwith the piston, a maximum input speed of a rotating shaft incommunication with the piston, a maximum input torque of a rotatingshaft in communication with the piston, a minimum input speed of arotating shaft in communication with the piston, a minimum input torqueof a rotating shaft in communication with the piston, or a maximumexpected temperature difference of air at each stage.

83. The method of claim 53 wherein controlling the operational parametercomprises controlling a timing of the transfer of air from the chamberto the pressure cell during the compression cycle.

84. The method of claim 53 wherein controlling the operational parametercomprises controlling a timing of the transfer of air from the pressurecell to the chamber during the expansion cycle.

85. The method of claim 54 wherein controlling the operational parametercomprises controlling a timing of a flow of liquid to the chamber.

86. The method of claim 56 wherein controlling the operational parametercomprises controlling a timing of a flow of liquid to the chamber.

87. The method of claim 53 wherein:

-   -   during the compression cycle, the piston is in communication        with a motor or a motor-generator; and    -   controlling the operational parameter comprises controlling an        amount of electrical power applied to the motor or the        motor-generator.

88. The method of claim 53 wherein:

-   -   during the expansion, cycle, the piston is in communication with        a generator or a motor-generator; and    -   controlling the operational parameter comprises controlling an        electrical load applied to the generator or the motor-generator.

89. The method of claim 54 wherein:

-   -   the liquid is flowed to the chamber utilizing a pump; and    -   controlling the operational parameter comprises controlling an        amount of electrical power supplied to the pump.

90. The method of claim 56 wherein:

-   -   the liquid is flowed to the chamber utilizing a pump; and    -   controlling the operational parameter comprises controlling an        amount of electrical power supplied to the pump.

91. The method of claim 53 wherein:

-   -   liquid in the pressure cell is circulated through a heat        exchanger that is in thermal communication with a fan; and    -   controlling the operational parameter comprises controlling an        amount of electrical power supplied to the fan.

92. The method of claim 53 further comprising placing the chamber incommunication with additional thermal energy during the expansion cycle.

93. The method of claim 92 wherein the additional thermal energy iswaste heat from another thermal source.

94. The method of claim 53 wherein controlling the operational parametercomprises controlling a compression ratio.

95. The method of claim 53 further comprising transferring compressedair within the pressure cell to a storage tank.

The following claims relate to a system.

96. An energy storage and recovery system comprising:

-   -   a first chamber having a moveable piston disposed therein and in        selective communication with an energy source;    -   a pressure cell in selective fluid communication with the first        chamber through a first valve;    -   an air source in selective fluid communication with the first        chamber through a second valve;    -   a liquid source in selective fluid communication with the first        chamber through a third valve; and    -   a controller in electronic communication with, and configured to        operate, system elements in one of the following states:    -   an intake step wherein the first valve is closed, the second        valve is open, and the third valve may be open or closed;    -   a compression step wherein the piston is in communication with        the energy source, the first and second valves are closed, the        third valve is open or closed, and then the first valve is        opened upon compression of the air in the chamber by the piston,    -   an expansion step wherein the piston is not in communication        with the energy source, the first valve is opened, the second        valve is closed, and the third valve may be open or closed, such        that the air expands in the chamber to move the piston, and then        the first valve is closed as the air continues to expand, and    -   an exhaust step wherein the piston is not in communication with        the energy source, the first valve is closed, the second valve        is open. and the third valve may be open or closed; and;    -   wherein the controller is configured to determine an operational        parameter in order to maintain a temperature of the air in the        first chamber within a range.

97. The energy storage and recovery system of claim 96 wherein themoveable piston comprises a solid piston.

98. The energy storage and recovery system of claim 96 wherein themoveable piston comprises a liquid piston.

99. The energy storage and recovery system of claim 96 furthercomprising a sprayer configured to inject the liquid into the air withinthe chamber.

100. The energy storage and recovery system of claim 99 wherein theliquid comprises water.

101. The energy storage and recovery system of claim 96 furthercomprising a bubbler configured to transfer heat between the liquid andair within the pressure cell.

102. The energy storage and recovery system of claim 101 wherein theliquid comprises water.

103. The energy storage and recovery system of claim 96 furthercomprising a sensor configured to detect a volume of liquid presentwithin the chamber, the sensor in electronic communication with thecontroller and referenced to determine the operational parameter.

104. The energy storage and recovery system of claim 96 furthercomprising a sensor configured to detect a property selected from thegroup comprising, a pressure, a temperature, a humidity, a position ofthe piston, a force on the piston. a liquid flow rate, a liquid level, aliquid volume, a speed of a shaft driven by the piston, or a torque ofthe shaft driven by the piston, wherein the sensor is in electroniccommunication with the controller and referenced to determine theoperational parameter.

105. The energy storage and recovery system of claim 96 furthercomprising a power generator or motor-generator configured to be inselective communication with the piston during the expansion stroke.

106. The energy storage and recovery system of claim 96 wherein thechamber is configured to be in thermal communication with a thermalenergy source.

107. The energy storage and recovery system of claim 96 furthercomprising a storage tank configured to receive compressed air from thepressure cell.

107a. The energy storage and recovery system of claim 96 wherein duringthe expansion the controller is configured to operate the first valve toinlet the air such that at an end of an expansion stroke of the piston,a pressure on the piston is substantially equal to a desired pressure.

107b. The method of claim 107a, wherein the desired pressure is an inputpressure of the next lowest pressure stage, or is ambient pressure.

107c. The method of claim 107a wherein the desired pressure iscalculated to maximize an efficiency of expansion.

107d. The method of claim 107a wherein the desired pressure iscalculated to produce a desired level of power output.

107e. The method of claim 107a wherein the desired pressure is withinapproximately 5 psi of an input pressure of the next lowest pressurestage.

The following claims relate to a system having multiple stages.

108. The energy storage and recovery system of claim 96, furthercomprising:

-   -   a second chamber having a moveable piston disposed therein and        in selective communication with the energy source; and    -   a second pressure cell in selective fluid communication with the        second chamber through a fourth valve, in selective fluid        communication with the first pressure cell through a fifth        valve, the fourth and fifth valves in communication with and        configured to be operated by the controller.

109. The energy storage and recovery system of claim 96, furthercomprising a plurality of a second chamber and second pressure cellconnected in series with the first chamber and first pressure cell, suchthat output from the first chamber is communicated to the secondchamber.

The following claims relate to a processor.

110. An apparatus for storing and recovering energy, the apparatuscomprising:

-   -   a host computer comprising a processor in electronic        communication with a computer-readable storage medium, the        computer readable storage medium having stored thereon one or        more codes to instruct the processor to,    -   receive a signal indicating a property of an energy storage and        recovery system comprising a first chamber having a moveable        piston disposed therein and in selective communication with an        energy source, and a pressure cell in selective fluid        communication with the first chamber, in response to the        received signal, control an element of the energy storage and        recovery system to maintain a temperature of air within the        first chamber within a temperature range.

111. The apparatus of claim 110 wherein the code stored on the computerreadable storage medium is configured to receive the signal indicating apressure in the pressure cell.

112. The apparatus of claim 110 wherein the code stored on the computerreadable storage medium is configured to receive the signal indicating apressure in the first chamber.

113. The apparatus of claim 110 wherein the code stored on the computerreadable storage medium is configured to receive the signal indicating atemperature of the air in the first chamber.

114. The apparatus of claim 110 wherein the code stored on the computerreadable storage medium is configured to receive the signal indicating atemperature of the air in the pressure cell.

115. The apparatus of claim 110 wherein the code stored on the computerreadable storage medium is configured to receive the signal indicating ahumidity of the air inlet to the first chamber.

116. The apparatus of claim 110 wherein the code stored on the computerreadable storage medium is configured to receive the signal indicating apower output.

117. The apparatus of claim 110 wherein the code stored on the computerreadable storage medium is configured to receive the signal indicating ahumidity of the air exhausted from the first chamber.

118. The apparatus of claim 110 wherein the code stored on the computerreadable storage medium is configured to receive the signal indicating aposition of the piston.

119. The apparatus of claim 110 wherein the code stored on the computerreadable storage medium is configured to receive the signal indicating aforce on the piston.

120. The apparatus of claim 110 wherein the code stored on the computerreadable storage medium is configured to receive the signal indicating atemperature of liquid flowed to the chamber.

121. The apparatus of claim 110 wherein the code stored on the computerreadable storage medium is configured to receive the signal indicatingrate of flow of liquid to the chamber.

122. The apparatus of claim 110 wherein the code stored on the computerreadable storage medium is configured to receive the signal indicating alevel of liquid in the chamber.

123. The apparatus of claim 110 wherein the code stored on the computerreadable storage medium is configured to receive the signal indicatingvolume of liquid in the chamber.

124. The apparatus of claim 110 wherein the code stored on the computerreadable storage medium is configured to receive the signal indicating aspeed of a rotating shaft in communication with the piston.

125. The apparatus of claim 110 wherein the code stored on the computerreadable storage medium is configured to receive the signal indicatingtorque of a rotating shaft in communication with the piston.

126. The apparatus of claim 110 wherein in response to the receivedsignal, the code stored on the computer readable storage medium isconfigured to instruct the processor to control a timing of a transferof air from the chamber to the pressure cell during a compression cycle.

126a. The apparatus of claim 110 wherein in response to the receivedsignal, the code stored on the computer readable storage medium isconfigured to instruct the processor to control a timing of a transferof air from the pressure cell to the chamber during an expansion cycle.

127. The apparatus of claim 110 wherein in response to the receivedsignal, the code stored on the computer readable storage medium isconfigured to instruct the processor to control a timing of a transferof liquid to the chamber.

128. The apparatus of claim 110 wherein in response to the receivedsignal, the code stored on the computer readable storage medium isconfigured to instruct the processor to control the amount of liquidtransferred to the chamber.

129. The apparatus of claim 110 wherein in response to the receivedsignal, the code stored on the computer readable storage medium isconfigured to instruct the processor to control an electrical loadapplied to a generator or a motor-generator in communication with thepiston, during an expansion cycle.

130. The apparatus of claim 110 wherein in response to the receivedsignal, the code stored on the computer readable storage medium isconfigured to instruct the processor to control an electrical powerapplied to a motor or a motor-generator in communication with thepiston, during a compression cycle.

131. The apparatus of claim 110 wherein in response to the receivedsignal, the code stored on the computer readable storage medium isconfigured to instruct the processor to control an electrical powerapplied to a pump to flow liquid into the chamber.

132. The apparatus of claim 110 wherein in response to the receivedsignal, the code stored on the computer readable storage medium isconfigured to instruct the processor to control an electrical powerapplied to fans associated with a heat exchanger configured to receiveliquid from the pressure cell.

133. The apparatus of claim 110 wherein in response to the receivedsignal, the code stored on the computer readable storage medium isconfigured to instruct the processor to control a compression ratio.

The following claims relate to a multi-stage system.

134. An energy storage and recovery system comprising:

-   -   a first stage comprising a first element moveable to compress        air in the first stage, the first stage in selective fluid        communication with an ambient air supply through a first valve;    -   a final stage comprising a second element moveable to compress        air in the final stage, and moveable in response to expanding        air within the final stage, the final stage in selective fluid        communication with a compressed air storage tank through a        second valve;    -   a controller configured to determine an amount of liquid to be        injected into the first stage or the final stage to maintain a        temperature of air in the first stage or in the final stage        within a temperature range; and    -   a liquid source in communication with the controller and        configured to inject the determined amount of liquid into the        first stage or into the final stage.

135. The energy storage and recovery system of claim 134, wherein thefirst moveable element is also moveable in response to expanding airwithin the first stage.

136. The energy storage and recovery system of claim 134, wherein thefirst moveable element comprises a piston.

137. The energy storage and recovery system of claim 134, wherein thefirst moveable element comprises a screw.

138. The energy storage and recovery system of claim 134, wherein thefirst stage or the final stage comprises a pressure cell in selectivefluid communication with a chamber.

139. The energy storage and recovery system of claim 134, wherein thefirst stage is configured to transfer to, and receive compressed airfrom, the final stage through a third valve.

140. The energy storage and recovery system of claim 139, wherein thefirst stage comprises a first chamber having a first piston disposedtherein as the first moveable element, and the final stage comprises asecond chamber having a second piston disposed therein as the secondmoveable element, the first and final stages lacking a pressure cell.

141. The energy storage and recovery system of claim 134, furthercomprising an intermediate stage positioned in series and in selectivefluid communication between the first stage and the final stage, theintermediate stage comprising a third element moveable to compress airin the intermediate stage, and moveable in response to expanding airwithin the intermediate stage.

142. The energy storage and recovery system of claim 141, wherein thefirst moveable element is also moveable in response to expanding airwithin the first stage.

143. The energy storage and recovery system of claim 142, wherein thefirst stage comprises a first chamber having a first piston disposedtherein as the first moveable element, and the intermediate stagecomprises a second chamber having a second piston disposed therein asthe third moveable element.

144. The energy storage and recovery system of claim 141, wherein theintermediate stage comprises a first chamber having a first pistondisposed therein as the third moveable element, and the final stagecomprises a second chamber having a second piston disposed therein asthe second moveable element.

145. The energy storage and recovery system of claim 141, wherein thefirst stage, the intermediate stage, or the final stage comprises achamber in selective fluid communication with a pressure cell.

146. The energy storage and recovery system of claim 141, whereinconsecutive stages do not include a pressure cell.

147. The energy storage and recovery system of claim 141, furthercomprising additional intermediate stages positioned in series betweenthe first stage and the final stage.

148. The energy storage and recovery system of claim 134, wherein thesecond moveable element comprises a piston.

149. The energy storage and recovery system of claim 148, wherein thesecond moveable element comprises a liquid piston.

150. The energy storage and recovery system of claim 148, wherein thesecond moveable element comprises a solid piston.

151. The energy storage and recovery system of claim 134, wherein acompression ratio of the first stage is larger than a compression ratioof the final stage.

152. The energy storage and recovery system of claim 141, wherein acompression ratio of the first stage is larger than a compression ratioof the intermediate stage, and the compression ratio of the intermediatestage is greater than a compression ratio of the final stage.

153. The energy storage and recovery system of claim 134, wherein theliquid comprises water.

154. A method of storing energy, the method comprising:

-   -   receiving ambient air in a first stage;    -   compressing the ambient air in the first stage;    -   transferring compressed air to a final stage;    -   further compressing air in the final stage;    -   transferring the further compressed air from the final stage to        a storage tank; and    -   determining an operational parameter to maintain a temperature        change of air in the first stage or in the second stage within a        range during the compression or the further compression.

155. The method of claim 154 wherein the determined operationalparameter comprises a timing of opening or closing valves controllingmovement of air into or out of the stages.

156. The method of claim 154 wherein the determined operationalparameter comprises an amount of liquid injected into the first stage orinto the final stage during the compression or the further compression.

157. The method of claim 154 wherein compressing the ambient aircomprises placing a piston disposed within a chamber of the first stage,in communication with an energy source.

158. The method of claim 154 wherein compressing the ambient aircomprises placing a screw disposed within a chamber of the first stage,in communication with an energy source.

159. The method of claim 154 wherein compressed air is transferred tothe final stage via an intermediate stage in which additionalcompression takes place.

160. The method of claim 154 further comprising:

-   -   transferring compressed air from the storage tank to the final        stage;    -   allowing the compressed air to expand and drive a first moveable        element in the final stage;    -   transferring air from the final stage to the first stage;    -   allowing compressed air in the first stage to expand and drive a        second moveable element in the first stage; and    -   determining an operational parameter to maintain a temperature        change of air in the first stage or in the second stage within a        range, during expansion of air within the first stage or within        the second stage.

161. The method of claim 160 wherein the determined operationalparameter comprises a timing of opening or closing valves controllingmovement of air into or out of the stages.

162. The method of claim 160 wherein the determined operationalparameter comprises an amount of liquid injected into the first stage orinto the final stage during expansion of air within the first stage orthe second stage.

163. The method of claim 160 wherein the first moveable elementcomprises a piston.

164. The method of claim 160 wherein the second moveable elementcomprises a piston.

165. The method of claim 160 wherein air is transferred from the finalstage to the first stage via an intermediate stage wherein furtherexpansion of air takes place.

What is claimed is:
 1. An apparatus comprising: a piston moveable withina cylinder to compress gas within the cylinder; a rotating shaftconfigured to drive the piston via a linkage; a source of shaft torquein communication with the rotating shaft a nozzle configured to effectgas-liquid heat exchange in the cylinder; and a host computer comprisinga processor in electronic communication with a non-transitorycomputer-readable storage medium, the non-transitory computer readablestorage medium having stored thereon one or more codes to instruct theprocessor to, receive a first input signal; calculate an efficiency fromthe first input signal; and based upon the efficiency, control anoperational property.
 2. The apparatus of claim 1 wherein theoperational property comprises a timing of a valve.
 3. The apparatus ofclaim 2 wherein the valve is configured to selectively exhaustcompressed gas from the cylinder.
 4. The apparatus of claim 3 whereinthe non-transitory computer readable storage medium has code storedthereon to instruct the processor to control the timing of the valve toexhaust the compressed gas at a higher pressure at an expense ofefficiency.
 5. The apparatus of claim 3 wherein the non-transitorycomputer readable storage medium has code stored thereon to instruct theprocessor to control the timing of the valve to exhaust the compressedgas at a lower pressure when a greater efficiency is desired for a givencompression cycle.
 6. The apparatus of claim 3 wherein thenon-transitory computer readable storage medium has code stored thereonto instruct the processor to control the timing of the valve to exhaustcompressed gas from the cylinder when a pressure within the cylinder isapproximately equal to a pressure of a next higher pressure stage or toa storage pressure.
 7. The apparatus of claim 1 wherein the source ofshaft torque comprises a motor.
 8. The apparatus of claim 7 wherein theoperational parameter comprises a power to the motor.
 9. The apparatusof claim 1 wherein the input comprises a signal indicating a torque ofthe rotating shaft.
 10. The apparatus of claim 1 wherein the inputcomprises a signal indicating a gas pressure.
 11. The apparatus of claim1 wherein the piston comprises a solid piston.
 12. The apparatus ofclaim 1 wherein the linkage comprises a piston rod.
 13. The apparatus ofclaim 12 wherein the piston rod is connected to the rotating shaftcomprising a crankshaft.
 14. The apparatus of claim 13 wherein thepiston is single-acting.
 15. The apparatus of claim 13 wherein thepiston is double-acting.
 16. The apparatus of claim 1 wherein the pistoncomprises a liquid.
 17. The apparatus of claim 1 wherein the linkagecomprises a hydraulic liquid.
 18. The apparatus of claim 2 wherein thetiming of the valve is controlled according to a desired compressionratio.
 19. The apparatus of claim 1 wherein the input comprises a liquidtemperature.
 20. The apparatus of claim 1 wherein the input comprises anoutput temperature.